Phase or frequency modulation



June 14, 1949.

D. WEIGHTON 2,473,318

PHASE OR FREQUENCY MODULATION Filed Aug. 7, 1947 A c .D E Y F FIRST PHASE SEKOND RYS A FRcE C) c T L FREQUENCY 5H1! TI/V6 FPEQUE/W Y ON 0 17 C TR L CHANGER N TMDRK CHAIVOER NU WE FPEGUENC V MODUL flTEO OSCILLA Invenlor ynmw NeigMon Patented June 14, 1949 PHASE R FREQUENCY MODULATION I Donald Weighton, Cambridge, England, asslgnor tol'ye Limited, Cambridge, England Application August '1. 1941, Serial No. 767,117

In Great Britain December 22, 1939 I V Section 1, Public 890, August 8, 1946 Patent expires December 22, 1959 Claims. (Cl. 332-22) The present invention relates to a method of phase or frequency modulation.

According to the present invention, the method of phase or frequency modulation consists in heterodyning master oscillator oscillations with frequency modulated oscillations, and then heterodyning the beat oscillations (comprising either the summation ordifference components) with the frequency modulated oscillations, and in submitting the frequency modulated oscillations in one .of the channels leading to the second heterodyning stage to the action of a phase shifting device or network.

According to a feature of the invention, the method consists in heterodyning master oscillator oscillations with frequency modulated oscillations, and then heterodyning the beat oscillations with the frequency modulated oscillations, the frequency modulated oscillations submitted to the first heterodyning, or the beat oscillations or frequency modulated oscillations submitted to the second heterodyning also being submitted to the action of a phase shifting device or network.

In order that the invention may be more clearly understood, an embodiment thereof will now be described, by way of example, with reference to the accompanying drawing which shows a schematic circuit diagram of an apparatus for carrying out the invention.

Referring to the drawing, the arrangement for carrying out the method consists of a master oscillator A, which may be crystal controlled, and

I an unstabilised oscillator 13 which is frequency modulated by a capacitor valve or similar device. 1

The outputs from both oscillators are fed into a first frequency changer C, which may comprise a valve, and the summation components in the output are selected. The selected signal is thus frequency modulated about a mean equal to the sum of the frequencies of the master and modulated oscillators. This signal is applied to a phase shifting deviceor network D which may consist of a balanced transmission line or, more conveniently, of an artificial network representing such a line. Thereby the voltage appearing across the termination of the network D undergoes a phase shift which is a linear function of the frequency whilst the amplitude is independent of the frequency.

The signal is, therefore, now phase modulated at the desired modulation frequency, in addition to thefrequency modulation derived from the modulated oscillator B. This frequency modulation may be removed by heterodyning the signal again with the output from the modulated'oscillator B by means of a second frequency changer 'E, and selecting the difference component. The

frequency of this component will be that of. the original crystal control master oscillator A, unaffected by any changes in the modulated oscil-g lator B but'having a phase modulation derived from the phase shifting network D. The extent of phase shift introduced is determined by the frequency excursions of the modulated oscillator B and the characteristic of the phase shifting network D, so thatby making this a sufficiently long balanced line, the phase shift may be increased to any desired magnitude.

The output from the second frequency changer E may be fed to one or more frequency multi pliers F.

The arrangement may be used as a frequency modulator by the introduction of a suitable distorting network in the modulationcircuit prior to the modulated oscillator B.

It will be understood that various modifications may be made without departing from the scope of the invention. For example the arrangement may be modified by introducing the phase shifting network D between the frequency modulated oscillator B and the first frequency changer C, or alternatively, between the frequency modulated oscillator B and the second frequency changer E.

The chief advantages of the method according to this invention are its inherent freedom from amplitude modulation and the absence of any theoretical limit to the modulation index. This may be increased to any desired magnitude thus avoiding the necessity for a large number of free quency multiplying stages in the design of a transmitter.

Iclaim:

1. Method of wave modulation which comprises heterodyning master oscillations of substantially constant frequency with frequency modulated oscillations, heterodyning the resultant beat oscillations with the frequency modulated oscillations, applying a phase shift which is a linear function of frequency to the frequency modulated oscillations prior to the second-mentioned heterodyning. and selecting a desired product of said second heterodyning.

2. Method as defined in claim 1, and further comprising subjecting said product to frequency multiplication.

3. Method of phase modulation which comprises heterodyning master oscillations of substantially constant frequency with frequency modulated oscillations, heterodyning the. resultant beat oscillations with the frequency moduconstant frequency with lated oscillations, applying a phase shift which; a linear function of frequency tothe frequency modulated oscillations prior to the second-memtioned heterodyning, and selecting a product of said second heterodyning having the original master oscillation in acordance with of the original frequency modulated oscillations. 4. Method of wave modulation which comprises frequency modulated in phase I heterodyning master-oscillations of substantially constant frequency with frequency modulated os cillations, applying a phase shift which is a linear function of frequency to the resultant beat oscillations, heterodyning the beat oscillations with the frequency modulated oscillations, and selecting a desired productof the second-mentioned heterodyning.

5. Method of wave modulation which comprises heterodyning master oscillations of substantially constant frequency with frequency modulated oscillations, selecting the summation beat oscilby said heterodyning, applying lations produced the modulation in frequency a phase shift which is a linear function of frequency to said beat oscillations, heterodyning the product of said phase shift with said 'frequency modulated oscillations, and selecting the difference component from the product of the second-mentioned heterodyning,

6. Method as defined in claim 5, and'further comprising subjecting said difierence component to frequency multiplication.

'7. Method of wave modulation which comprises applying a phase delay which is a linear function of frequency to frequency modulated oscillations, heterodyning master oscillations of substantially the delayed frequency modulated oscillations, heterodyning the resultant beat oscillations with undelayed frequency 1 modulated oscillations, and selecting a desired product of the second-mentioned heterodyning.

8. Method of wave applying a phase delay which is a linear function of frequency to frequency modulated oscillations.

heterodyning master oscillations of substantially constant frequency with the delayed frequency modulated 7 beat oscillations from the product of said heterodyning. heterodyning the selected beat oscillations withundelayed frequency modulated oscillations, and selecting the difference component of the product of the second-mentioned heterodyning.

9. Method of wave modulation which comprises heterodyning master oscillations of substantially constant frequency with frequency modulated oscillations, heterodyning the resultant beat oscillations with frequency modulated oscillations delayed in phase as a linear function of frequency, and selecting a desired product of the secondmentioned heterodyning.

10. Method of wave modulation which comprises heterodyning master oscillations of substantially constant frequency with frequency modulated oscillations, selecting the summation beat oscillations from the product of said heterodyning, heterodyning the summation beat oscillations with frequency modulated oscillations altered in phase as a linear function of frequency, and selecting the difference component from the product of the second-mentioned heterodyning.

DONALD WEIGHTON.

' REFERENCES CITED The following references are of record in the file of this patent: V

UNITED STATES PATENTS Number Name Date 1,964,522 Lewis June 26, 1934 2,335,934 Goldstine Dec. 7, 1943 modulation which comprises oscillations, selecting the summation 

